122 THE VEGETATIVE ORGANS 



to twenty (see Figs. 70, 189, 194). If the growth of 

 the axis above such dormant buds is arrested by injury 

 or removal, the dormant buds begin to grow into leafy 

 shoots. Thus old branches, and even trunks of trees, may 

 become covered with fresh shoots. 



Shoots arising on the trunks of trees, usually from buds 

 which have long been dormant, are known as ' stool shoots ', 

 and are common on trees with a thin bark, e. g. the Lime. 

 They are a characteristic feature of the Elm, and occur 

 frequently on Sycamores, Oaks, and many other trees. 



New buds are occasionally formed in the outer tissues 

 of branches and other members, e. g. on roots and leaves, 

 and not in leaf-axils ; such buds are termed adventitious 

 buds. True dormant buds have a pith continuous with 

 that of the branch, while the pith of adventitious buds is 

 not continuous. Adventitious shoots are common on the 

 roots of shrubs and trees, e. g. Raspberry (Fig. 27), Rose, 

 and Poplar, also on the roots of Dandelion ; while some 

 Ferns produce adventitious buds on their leaves. 



Shedding of leaves and branches. Having now described 

 the structure and behaviour of buds, we may conclude this 

 chapter with a reference to the shedding of leaves and 

 branches. The shedding of scale-leaves is a noteworthy 

 feature in the spring, when, under Sycamores and Beeches, 

 the ground is covered with them. In the autumn the 

 foliage-leaves are thrown off and again the ground is 

 covered. Thus we have at least two leaf-falls in a year : 

 (1) A spring fall of scale-leaves ; and (2) an autumn fall 

 of foliage-leaves. From the Pine and often the Poplar 

 whole branches are thrown off. In addition there is the fall 

 of flowers, fruits, and their axes, so that each year a tree 

 sheds many of its organs. 



